喜欢Stack的人......
我正在尝试让我的应用程序使用EditText框保存文本，以便当用户关闭应用并重新打开它时，输入字段会保留，但点击时我会收到NPE我的按钮。
请帮助我：）
package com.smarte.smartipcontrol;
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
public class IPEntry extends Activity {
public final static String ACTUALSMARTIP = "com.smarte.smartipcontrol.ACTU_IP";
private EditText editText;
private EditText editText2;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.act_ipentry);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.act_ipentry, menu);
return true;
}
/** Called when the user clicks the SendIP button */
public void sendip(View view) {
Intent intent = new Intent(this, IPControl.class);
EditText editText = (EditText) findViewById(R.id.serverIpAddress);
String actu_ip = editText.getText().toString();
intent.putExtra(ACTUALSMARTIP, actu_ip);
startActivity(intent);
}
protected void onResume() {
super.onResume();
SharedPreferences prefs = getPreferences(0);
String restoredText = prefs.getString("text", null);
if (restoredText != null) {
editText.setText(restoredText, TextView.BufferType.EDITABLE);
int selectionStart = prefs.getInt("selection-start", -1);
int selectionEnd = prefs.getInt("selection-end", -1);
if (selectionStart != -1 && selectionEnd != -1) {
editText.setSelection(selectionStart, selectionEnd);
}
SharedPreferences prefs2 = getPreferences(1);
String restoredText2 = prefs2.getString("text2", null);
if (restoredText2 != null) {
editText2.setText(restoredText2, TextView.BufferType.EDITABLE);
int selectionStart2 = prefs2.getInt("selection-start2", -1);
int selectionEnd2 = prefs2.getInt("selection-end2", -1);
if (selectionStart2 != -1 && selectionEnd2 != -1) {
editText2.setSelection(selectionStart2, selectionEnd2);
}
}
}
}
protected void onPause() {
super.onPause();
SharedPreferences.Editor editor = getPreferences(0).edit();
editor.putString("text", editText.getText().toString());
editor.putInt("selection-start", editText.getSelectionStart());
editor.putInt("selection-end", editText.getSelectionEnd());
editor.commit();
SharedPreferences.Editor editor2 = getPreferences(1).edit();
editor2.putString("text2", editText2.getText().toString());
editor2.putInt("selection-start2", editText2.getSelectionStart());
editor2.putInt("selection-end2", editText2.getSelectionEnd());
editor2.commit();
}
}
logcat的
12-17 13:20:20.043: E/AndroidRuntime(1069): FATAL EXCEPTION: main
12-17 13:20:20.043: E/AndroidRuntime(1069): java.lang.RuntimeException: Unable to pause activity {com.smarte.smartipcontrol/com.smarte.smartipcontrol.IPEntry}: java.lang.NullPointerException
12-17 13:20:20.043: E/AndroidRuntime(1069): at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3016)
12-17 13:20:20.043: E/AndroidRuntime(1069): at android.app.ActivityThread.performPauseActivity(ActivityThread.java:2971)
12-17 13:20:20.043: E/AndroidRuntime(1069): at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:2949)
12-17 13:20:20.043: E/AndroidRuntime(1069): at android.app.ActivityThread.access$800(ActivityThread.java:141)
12-17 13:20:20.043: E/AndroidRuntime(1069): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1245)
12-17 13:20:20.043: E/AndroidRuntime(1069): at android.os.Handler.dispatchMessage(Handler.java:99)
12-17 13:20:20.043: E/AndroidRuntime(1069): at android.os.Looper.loop(Looper.java:137)
12-17 13:20:20.043: E/AndroidRuntime(1069): at android.app.ActivityThread.main(ActivityThread.java:5039)
12-17 13:20:20.043: E/AndroidRuntime(1069): at java.lang.reflect.Method.invokeNative(Native Method)
12-17 13:20:20.043: E/AndroidRuntime(1069): at java.lang.reflect.Method.invoke(Method.java:511)
12-17 13:20:20.043: E/AndroidRuntime(1069): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
12-17 13:20:20.043: E/AndroidRuntime(1069): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
12-17 13:20:20.043: E/AndroidRuntime(1069): at dalvik.system.NativeStart.main(Native Method)
12-17 13:20:20.043: E/AndroidRuntime(1069): Caused by: java.lang.NullPointerException
12-17 13:20:20.043: E/AndroidRuntime(1069): at com.smarte.smartipcontrol.IPEntry.onPause(IPEntry.java:72)
12-17 13:20:20.043: E/AndroidRuntime(1069): at android.app.Activity.performPause(Activity.java:5206)
12-17 13:20:20.043: E/AndroidRuntime(1069): at android.app.Instrumentation.callActivityOnPause(Instrumentation.java:1226)
12-17 13:20:20.043: E/AndroidRuntime(1069): at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3002)
12-17 13:20:20.043: E/AndroidRuntime(1069): ... 12 more
答案 0 :(得分：3)
我从来没有看到你实例化editText2，一旦你检查第72行，你就可能会得到认可：at com.smarte.smartipcontrol.IPEntry.onPause(IPEntry.java:72)（也可以是editText，看看我的编辑）。
由于editText和editText2（顺便说一下名称选择不当）是全局变量，因此您应该在onCreate()中实例化它们：
editText = (EditText) findViewById(R.id.serverIpAddress);
editText2 = (EditText) findViewById(R.id.theSecondEditText);
修改：顺便说一下，在sendIp您要实例化本地变量editText，这意味着不仅editText2是null，editText也是null！您应 从不 同时具有相同名称的全局变量和局部变量（构造函数除外，然后使用this关键字）。
答案 1 :(得分：2)
我怀疑问题是你永远不会实例化editText2，所以当你尝试在其上调用getText()来检索要存储的值时它为空。
在一个不相关的注释中：editText和editText2对于变量名称来说真的很糟糕。您应该始终努力使您的变量名称具有足够的描述性，以便您可以在不必寻找的情况下告诉它们是什么。也许你应该为其中一个考虑ipEntryTxt之类的东西？
编辑：还请注意您应该移动此行：
EditText editText = (EditText) findViewById(R.id.serverIpAddress);
在onCreate（）内而不是在sendip()内。如果用户打开此活动但是从不按下按钮（调用sendip（）），那么你的代码就是现在，那么editText将为null当onPause（）触发时，它也会给你一个空指针异常。